.|  Baltimore Ecosystem Study
Ecological importance of organic carbon, nitrogen, and phosphorus in watersheds affected by land use and climate change
Carbon, nitrogen and phosphorus are elements necessary to the creation and persistence of life. Previous work shows that organic forms of C, N, and P can comprise a substantial proportion of the total N and P in surface waters (Kaushal and Lewis 2003, Kaushal and Lewis 2005, Pellerin et al. 2006). Yet, the cycling of organic N and P has been poorly incorporated into existing paradigms of nutrient cycling due to a lack of knowledge regarding generation and metabolism.
 
Our work at the Baltimore Ecosystem Study LTER shows that biologically reactive forms of organic C, N, and P can be generated in great quantity across gradients of land use in the Chesapeake Bay watershed (Kaushal et al. in review; Duan et al. submitted). Elevated urban stream metabolism and change in increases in dissolved organic matter composition with urbanization occurred along the suburban/urban gradient of the Gwynns Falls watershed (Kaushal et al. in review). Leaf litter from riparian forest and periphyton on streambed provide considerable amount of organic C, N and P that are bioavailable to stream microbes for nitrogen transformation (Newcomer et al. 2012; Duan et al. submitted). Warming associated with urbanization and climate changes can increase carbon and nutrient fluxes from sediments of urban streams (Duan and Kaushal 2013). Although not typically quantified, organic forms of carbon, nitrogen, and phosphorus may be an important supply of nutrients contributing to eutrophication, and changes in the abundance of inorganic vs. organic nutrients can be an important predictor of microbial community structure and function (Findlay and Sinsabaugh 2006, Kaushal et al. In preparation). Continuing work also focuses on comparing and understanding dynamics of inorganic carbon in watersheds (Kaushal et al. 2013).
 


 
Figure 1. Estimates of average gross primary production from monthly measurements along 4 main sampling stations along the Gwynns Falls (GFGL, GFGB, GFVN, GFCP) and nearby forest reference watersheds of the Baltimore LTER site (POBR, BARN).

 


 
Figure 2. Plots of DOC flux from sediment, or changes in protein-like fluorescence, humic-like fluorescence and their (P/H) ratio versus incubation temperature across a land use gradient.

 

Preparative scale column chromatography to isolate chemical fractions of dissolved organic matter for chemical and isotopic analyses. Photo: Sujay Kaushal


Leucine incorporation and epifluorescent microcoscopy to determine bacterial production of microbes on different organic matter sources.


Short-term incubations to measure uptake of inorganic and organic nutrients in streams during ambient temperatures. Photo: Sujay Kaushal

References
Duan, S.W., and S.S. Kaushal. 2013. Warming increases carbon and nutrient fluxes from sediments in streams across land use. Biogeosciences 10: Biogeosciences, 10, 1193-1207. doi:10.5194/bg-10-1193-2013.
 
Duan, S.W., K. Delaney, S.S. Kaushal, S.E.G. Findlay and K. Belt. 2013. Potential Impacts of Leaf Litter on Water Quality in Urbanized Watersheds. Biogeochemistry, Submitted.
 
Findlay, S., R.L. Sinsabaugh. 2006. Large-scale variation in subsurface stream biofilms: a cross-regional comparison of metabolic function and community similarity. Microbial Ecology 52: 491-500.
 
Kaushal, S. S., K. Delaney-Newcomb, S. E. G. Findlay, T. A. Newcomer, S. Duan, M. J. Pennino, G. M. Sivirichi, A. M. Sides-Raley, M. R. Walbridge, K. T. Belt. Longitudinal changes in carbon and nitrogen fluxes and stream metabolism along the urban watershed continuum. Biogeochemistry. In Review.
 
Kaushal, S.S., G.E. Likens, R. Utz, M.L. Pace, M. Grese, and M. Yepsen. 2013. Increased river alkalinization in the Eastern U.S. Environmental Science & Technology DOI: 10.1021/es401046s
 
Kaushal, S.S. and W.M. Lewis, Jr. 2003. Patterns in the chemical fractionation of organic nitrogen in Rocky Mountain streams. Ecosystems 6: 483-492.
 
Kaushal, S.S. and W.M. Lewis, Jr. 2005. Fate and transport of dissolved organic nitrogen in minimally disturbed streams of the Colorado Rockies. Biogeochemistry 74: 303-321.
 
Newcomer, T.A., S.S. Kaushal, P.M. Mayer, A. Shields, E.A. Canuel, P.M. Groffman, A.J. Gold, and K.A. Delaney. 2012. Influence of natural and novel organic carbon sources on denitrification in forest, urban degraded, and restored streams. Ecological Monographs doi:10.5061/dryad.4gk00/1.
 
Pellerin, B., S.S. Kaushal, and W.H. McDowell. 2006. Does anthropogenic nitrogen enrichment increase organic nitrogen concentrations in runoff from forested and human-dominated watersheds? Ecosystems 9: 852-864.
 
This research was supported by funding from the NSF Long-term Ecological Research (LTER) Program. This material is based upon work supported by the National Science Foundation under Grant No. 1027188. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.